Various actuators are known. The term actuator as used herein refers to a device that converts electrical energy into mechanical motion, in particular, for moving a load. For example, so-called “inch worms” are known actuators. Inch worm actuators come in many forms and variations, including piezoelectric, magnetostrictive, electromagnetic, and shaped memory alloy, for example.
However, piezoelectric/electrostrictive “inch worms” have difficulties with their clamps, both in reaching their clamp races and in the excessive voltage required to drive these clamps. They also have problems due to reduced piezoelectric motion at the low temperatures such as are encountered in outer space operations, for example. Magnetostrictive “inch worms” also have difficulties with their clamps in reaching their races. Their performance does not degrade in low temperatures but, they are, unacceptably large and bulky due to their coils and mechanical preload structure. Electromagnetic “inch worms” are also large and bulky, typically do not hold position with power off and have trouble holding with their clamps. “Inch worms” in general, also typically have difficulties with “glitches” as they grasp and release during steps.
Motorized screws are known actuators. These come in many forms and variations including piezoelectric, from traveling wave and oscillatory, to one way drives, such as picomotors. These also include electromagnetic motors driving screws through a speed reducing transmission, and the electromagnetic equivalent of picomotors.
However, piezoelectric/electrostrictive motorized screws have problems associated with poor performance of the piezoelectric/electrostrictive materials in the cold temperatures of outer space operations, for example. The electromagnetic equivalent of motorized screws has the problem of achieving precise, repeatable very small steps. The small stroke of the piezo crystal helps in this respect. Electromagnetic motorized screws also tend to be large due to the windings.
Voice coils are also known actuators. However, voice coils typically do not hold position with power off, and they are relatively large and bulky.
Linear electromagnetic motors are also known actuators. However, linear electromagnetic motors typically do not hold position with power off.
Direct expansion/contraction piezoelectric/electrostrictive actuators (very short stroke) are also known actuators. However, these actuators typically do not have sufficient cumulative stroke and are limited in their cold temperature performance.
Therefore, a need exists for an improved actuator that overcomes the problems, drawbacks and limitations of the known actuators, such as those mentioned above.